Darkened skin is most often harmless, but in a few cases it can be a symptom of a serious disease. The cells that are responsible for skin color are called melanocytes and are found in the epidermis or outermost layer of skin. They produce and distribute a substance called melanin, a protein pigment that is dark in color and serves mainly as a form of protection from the ultraviolet rays of the sun. A person's skin color is the result of the amount of protein the melanocytes produce.

When too much melanin is manufactured, the skin darkens. The darkening may be widespread or confined to specific areas of, the body, depending upon the cause.

Causes of darkened skin

Addison's diseaseThis is a disorder in which the adrenal glands fail to produce adequate steroid hormones. The underlying cause remains unknown, but the condition is sometimes a complication of tuberculosis, cancer, pituitary disease, or prolonged use of steroid drugs such as cortisone. The symptoms can be controlled with medication (usually cortisone) to replace the missing adrenal hormones. However, there is no cure for the disease, which can be fatal if it is untreated or the replacement hormones are stopped.

Brownish skin that appears to be suntanned and that may have patches of white is a characteristic symptom. The disease also darkens freckles, scars, and nipples. Other symptoms include weakness and fatigue, hair loss, feeling cold at all times, low blood pressure that can cause faintness and dizziness, and gastrointestinal disturbances such as nausea, vomiting, diarrhea, stomach pains, and loss of appetite and weight. People with Addison's disease also often experience mood swings and changes in their normal behavior, sometimes resulting in a misdiagnosis of psychological problems.

Skin darkening on the hands may be a sign of excessive iron.

Inflammatory skin disorders such as rosacea often result in a darkening of facial skin.

HyperpigmentationSkin darkening may occur because excessive melanin is being deposited in the epidermis or because the skin is generating large numbers of melanocytes. This change sometimes occurs in a condition called hemochromatosis, in which too much iron is present in the body. The skin may appear bronze in color, and other serious complications such as cirrhosis of the liver, diabetes, and heart problems may also be present.

LupusSystemic lupus erythematosus, often referred to simply as lupus, is an autoimmune disease in which the body's immune system mounts an attack against various organs. Lupus can affect almost every organ system, but the most com­mon manifestations are arthritis and darkening of the facial skin, usually in a butterfly-shaped pattern. The skin darkening and other symptoms are often exacerbated by exposure to the sun.

Oral contraceptivesThe use of oral contraceptives sometimes causes the skin of a woman's face to darken, usually in a characteristic butterfly pattern. This condition is called chloasma or melasma and is similar to the skin darkening that sometimes occurs during pregnancy. It consists of dark brown, symmetrical patches of pigmentation on the face, usually on the forehead, temples, and cheekbones. The skin on the abdomen and around the nipples may also darken. The darkening usually becomes more obvious when the skin is exposed to sunlight and gradually disappears after oral contraceptives are discontinued.

RosaceaThis is a chronic, inflammatory skin condition affecting mostly the face. It is characterized by pimples, persistent reddening or flushing of the skin, and a swollen, bulbous nose. In unusual cases, the skin changes also appear on the trunk, arms, and legs.

Sun exposureExcessive exposure to the sun is the most common cause of skin darkening. The darkening is due to the skin's increased production of melanin, which is a protective mechanism against the sun's harmful ultraviolet rays. In the last few decades, a suntan has been equated with a healthy, outdoor look, and large numbers of ordinarily fair-skinned people have deliberately exposed their skin to the sun to acquire suntans. This practice has led to an alarming rise in skin cancer, including malignant melanoma, which is often fatal. Fortunately, fashion is beginning to change, and deeply tanned skin is no longer considered chic.

Advice about darkened skin

Many common medications increase the skin's sensitivity to sun. These include antiacne medications, antibiotics, and drugs used to treat high blood pressure. If you notice that you sunburn more easily, ask your doctor or pharmacist if the increased sun sensitivity may be a reaction to your medication.

A darkening or other change in a mole is a common warning sign of skin cancer. Dermatologists urge that everyone practice regular skin self-examination, paying particular attention to moles that are exposed to the sun.

This article was last reviewed November 13, 2005 by Dr.
James Krider.Reproduced in part with permission of Home Health Handbook.